Here's my input.

C/C++: Either one, really. C++ is powerful, and its ability to make ADTs is useful; coming from perl, it should be relatively simple to learn the basics--though beyond that you're on your own(or so I figure; the other way around, C/C++ -> perl wasn't too difficult).

Assembly: Not only can this be used in C/C++ directly, via _asm(or __asm), i.e., the inline assembler, but it offers a *great* glimpse at the inner workings of the computer--not to mention that it is FAST. Even if you don't plan to program in assembly, learning it can help you write better code(boolean algebra, etc., check this site out for basics: http://webster.cs.ucr.edu/Page_asm/ ArtofAssembly/ArtofAsm.html